Thin laminated single pole perpendicular write head

ABSTRACT

Single write poles tend to large shape anisotropy which results in a very large remnant field when not actually writing. This has now been eliminated by giving the write pole the form of a three layer laminate in which two ferromagnetic layers are separated by a non-magnetic or antiferromagnetic coupling layer. Strong magnetostatic coupling between the outer layers causes their magnetization directions to automatically be antiparallel to one another, unless overcome by the more powerful write field, leaving the structure with a low net magnetic moment. The thickness of the middle layer must be carefully controlled.

This is a divisional application of U.S. patent application Ser. No.10/610,036, filed on Jun. 30, 2003, now U.S. Pat. No. 7,064,924, whichis herein incorporated by reference in its entirety, and assigned to acommon assignee.

FIELD OF THE INVENTION

The invention relates to the general field of magnetic disk systems withparticular reference to magnetic write heads for perpendicular designs,more specifically to remnant field reduction in single pole heads.

BACKGROUND OF THE INVENTION

Perpendicular magnetic recording (PMR) is important for the future ofthe magnetic recording industry because it offers higher areal densitythan the current longitudinal magnetic recording (LMR). This is due tothe fact that the PMR medium is thermally more stable than that used forLMR. At present, LMR has achieved over 100 Gigabits per square inch(Gbpsi) in the laboratory and more than 60 Gpsi in products currentlyoffered at the market place. In order to further extend the LMRrecording density, two main obstacles have to be overcome. The first oneis the thermal stability of the LMR recording media which arises becauseits thickness has to decrease to the extent that thermal energy couldrandomize the recorded bits. The second one is the ongoing increase inthe write field needed to record on the high coercivity LMR media.

This high coercivity is needed to achieve high bit resolution and goodthermal stability. Both obstacles to LMR would be considerably loweredif PMR were deployed instead. Thicker PMR media with a magnetically softunder-layer film (SUL) could be used to alleviate the thermal stabilityproblem. A PMR writer provides a larger write field than that of LMR,which is limited to the fringe field from its write gap.

An example of a perpendicular writer of the prior art is shown inFIG. 1. Magnetic yoke 11 is surrounded by write coil 12 and includesmain pole 13 that terminates as a write pole tip at the recordingsurface. Return pole 14 conveys the magnetic flux generated by coil 12down to a short distance from the recording surface. The flux passesfrom write pole 13 through recording layer 16, into SUL 17, and thenback up into return pole 14

Currently, the single pole is usually made of high Bs (saturation fluxdensity—measured in Teslas) material, with values >2T, and has verysmall dimensions (0.1 μm in width and 0.2 μm in thickness) together witha relatively long yoke. As a result, the single pole has very largeshape anisotropy. After the writing process, the remnant field from asingle pole can be very large (as high as 2 kOe), which usually causeserasure of written bits. This problem will get more severe with furtherdecreases in device dimensions.

A routine search of the prior art was performed with the followingreferences of interest being found:

In U.S. Pat. No. 5,477,007, Shukh et al describe a top pole having alaminated structure. In U.S. Pat. No. 6,278,590 Gill et al disclose alaminated pole. U.S. Pat. No. 6,396,735 (Michijima et al) shows alaminated memory element. Sasaki teaches that a top pole may belaminated of two or more materials in U.S. Pat. No. 6,255,040. In U.S.Pat. No. 5,621,592, Gill et al disclose a laminated Fe-based/NiMnstructure for a write pole while Mallary shows a vertically laminatedpole in U.S. Pat. No. 5,108,837. Note that all these references relateto LMR and are not applicable to perpendicular recording systems in theforms and dimensions described.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a magnetic writer suitable for vertical recording.

Another object of at least one embodiment of the present invention hasbeen that the write pole of said writer exhibit low remnantmagnetization when not in use.

Still another object of at least one embodiment of the present inventionhas been that said write pole provide a high write field as well as alow remnant magnetization.

A further object of at least one embodiment of the present invention hasbeen that manufacture of said write pole introduce no significantchanges to existing processes for manufacturing the writer.

These Objects have been achieved by giving the write pole the form of athree-layer laminate in which two ferromagnetic layers are separated byan anti-ferromagnetic coupling layer or by a non-magnetic layer. If anantiferromagnetic coupling layer is used, its thickness is chosen to beoptimum for antiferromagnetic coupling. In the remanent state (noexternal driving field), the two laminated ferromagnetic layers willstay antiparallel to each other so as to minimize the interlayerexchange coupling energy and to allow as much magnetic flux closure aspossible, leaving the structure with a low net magnetic moment. For thenon-magnetic layer, its thickness is chosen so that there can be noferromagnetic exchange coupling between the ferromagnetic layers, inwhich case the low net magnetic moment is achieved solely throughmagnetic flux closure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a vertical magnetic writer of the prior art.

FIG. 2 is the starting point for the method of the present invention,including the first layer of a three layer laminated write pole.

FIGS. 3 and 4 illustrate additional steps in forming the write pole.

FIG. 5 shows the completed device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

We will disclose the present invention by providing a description of amethod for generating it, thereby making the structure of the inventionapparent as well. Referring now to FIG. 2, the method begins with theprovision of magnetic yoke 11 which had previously been deposited andpatterned on return pole 14 which is shown in contact with substrate 21(commonly a magnetic shield).

Conductive coil 12 is also formed so that it surrounds yoke 11. Thevarious incidences of layer 31 that appear in the figure representinsulating, non-magnetic material that serves to provide mechanicalintegrity to the structure.

Normally, the next step would be to deposit the full thickness of thewrite pole. However, in a departure from the prior art, a first (lower)layer of ferromagnetic material 22 is deposited onto the topmost surfaceof 31 as well as onto the exposed surface of yoke 11, giving thestructure, at this stage, the appearance seen in FIG. 2. For lowerferromagnetic layer 22 we have preferred to use FeCo but other similarmaterials, such as CoNiFe, FeCoZrO, or any alloy of Fe and/or Co and/orNi that has a high B_(s) value could be substituted. Ferromagnetic layer22 is deposited to a thickness between about 500 and 2,000 Angstroms.

Now follows a key novel feature of the invention. As seen in FIG. 3,layer 23 is next deposited directly onto layer 22, followed by thedeposition onto itself of a second ferromagnetic layer 24. There are twopossible choices for layer 23 (representing two different embodiments ofthe invention):

(1) layer 23 is an antiferromagnetic coupling material. In this case,Its thickness is carefully chosen as needed for an effectiveantiferromagnetic coupling between layers 22 and 24. A wide range ofantiferromagnetic coupling materials is available, including Ru, Rh, andIr, but the choice of thickness will depend on which one is selected.For example, if the antiferromagnetic coupling layer is Ru it will needto be deposited to a thickness between about 3 and 10 Angstroms while ifit is Rh it will need to be deposited to a thickness between about 4 and7 Angstroms.

(2) layer 23 is a non-magnetic material such as Ta, NiCr, Cu, or Al₂O₃,with NiCr being preferred. Its thickness is between about 5 and 50Angstroms which is carefully chosen to be just thick enough to preventany exchange coupling between layers 22 and 24 but still thin enough toallow strong magnetostatic coupling between layers 22 and 24. As aresult, these two layers will automatically orient themselves so as tobe magnetically antiparallel to one another when no external field ispresent. However, in the presence of a strong external field, bothlayers will align themselves in the same direction and act as a singleunit.

Note that, as a further refinement, the coupling field between layers 22and 24 can be adjusted by insertion of a lower coercivity layer at theantiferromagnetic-ferromagnetic interface. For example, if layers 22 and24 are of CoFe, an adjusting layer of NiFe could be used (see examplesc, d, e, and f below).

After the deposition of one or other of the two versions of layer 23,upper ferromagnetic layer 24 is laid down to a thickness between about500 and 2,000 Angstroms. Suitable materials for layer 24 include CoNiFe,FeCo, and other high B_(s) alloys of Fe, Co, and Ni, with FeCo beingpreferred. Preferably, but not critically, layers 22 and 24 will havethe same thickness and be of the same material.

Moving on to FIG. 4, with the laminate of layers 22-23-24 in place,formation of the device is completed by patterning these three layerstogether to form a laminated write pole that extends from yoke 11 in thesame direction as return pole 14, terminating at a surface that iscoplanar with the corresponding surface of the return pole, giving thecompleted device the appearance illustrated in FIG. 5.

We have determined that, provided the materials and thickness ranges areas disclosed above, the resulting laminated write poles have residualfluxes that are less than about 0.1T, while at the same time being ableto provide a write field of at least 10 kOe.

We list below several examples of the laminate structure includingaddition of NiFe for fine adjustment (thicknesses in Angstroms):

-   a. COFe1000/RU3/CoFe1000-   b. CoFe1000/Rh6/CoFe1000-   c. CoFe1000/Ru3/NiFe2-4/CoFe1000-   d. CoFe1000/NiFe2-4/Ru3/NiFe2-4/CoFe1000-   e. CoFe1000/Rh6/NiFe2-4/CoFe1000-   f. CoFe1000/NiFe2-4/Rh6/NiFe2-4/CoFe1000

1. A method to manufacture a perpendicular magnetic writer, comprising:providing a magnetic yoke having a bottom surface and an exposed topsurface, said bottom surface being magnetically connected to a returnpole; providing a conductive coil that surrounds said yoke; depositing alower layer of ferromagnetic material onto an area that includes saidfront surface; depositing a layer of antiferromagnetic coupling materialon said lower layer; depositing an upper ferromagnetic layer on saidlayer of non-magnetic material whereby there is antiferromagneticcoupling between said upper and lower ferromagnetic layers; patterningsaid upper and lower ferromagnetic layers, as well as saidantiferromagnetic layer, to form a laminated write pole that extendsfrom said yoke in the same direction as the return pole and that has abottom surface that is coplanar with that of said return pole; andwhereby said laminated write pole has a residual flux that is less thanabout 0.1 T.
 2. The method described in claim 1 wherein said lowerferromagnetic layer is selected from the group consisting of FeCo,CoNiFe, and any alloy containing Co, Fe, or Ni and having a high Bsvalue.
 3. The method described in claim 1 wherein said lowerferromagnetic layer is deposited to a thickness between about 500 and2,000 Angstroms.
 4. The method described in claim 1 wherein said upperferromagnetic layer is FeCo, CoNiFe, and any alloy containing Co, Fe, orNi and having a high Bs value.
 5. The method described in claim 1wherein said upper ferromagnetic layer is deposited to a thicknessbetween about 500 and 2,000 Angstroms.
 6. The method described in claim1 wherein said antiferromagnetic coupling layer is Ru, Rh, or Ir.
 7. Themethod described in claim 1 wherein said antiferromagnetic couplinglayer is Ru which is deposited to a thickness between about 3 and 10Angstroms.
 8. The method described in claim 1 wherein saidantiferromagnetic coupling layer is Rh which is deposited to a thicknessbetween about 3 and 7 Angstroms.
 9. The method described in claim 1wherein said laminated write pole can provide a write field of at least10 kOe.
 10. The method described in claim 1 further comprisingdepositing a layer of NiFe between said lower ferromagnetic layer andsaid antiferromagnetic coupling layer whereby antiferromagnetic couplingbetween said upper and lower ferromagnetic layers may be preciselycontrolled.
 11. The method described in claim 1 further comprisingdepositing a layer of NiFe between said antiferromagnetic coupling layerand said upper ferromagnetic layer whereby antiferromagnetic couplingbetween said upper and lower ferromagnetic layers may be preciselycontrolled.
 12. A perpendicular magnetic writer, comprising: a magneticyoke having first and second ends, said second end being magneticallyconnected to a return pole that extends away from said yoke in adirection; a conductive coil that surrounds said yoke; a write pole thatextends from said yoke's first end in the same direction as the returnpole and that has a bottom surface that is coplanar with that of saidreturn pole; said write pole being a laminate of upper and lowerferromagnetic layers separated by a layer of antiferromagnetic couplingmaterial, there being no other layers in said laminate; and there beingantiferromagnetic coupling between said upper and lower ferromagneticlayers whereby said laminated write pole has a residual flux densitythat is less than about 0.1T.
 13. The magnetic writer described in claim12 wherein said lower ferromagnetic layer is selected from the groupconsisting of FeCo, CoNiFe, and any alloy containing Co, Fe, or Ni andhaving a high Bs value.
 14. The magnetic writer described in claim 12wherein said lower ferromagnetic layer has a thickness between about 500and 2,000 Angstroms.
 15. The magnetic writer described in claim 12wherein said upper ferromagnetic layer is selected from the groupconsisting of FeCo, CoNiFe, and any alloy containing Co, Fe, or Ni andhaving a high Bs value.
 16. The magnetic writer described in claim 12wherein said upper ferromagnetic layer has a thickness between about 500and 2,000 Angstroms.
 17. The magnetic writer described in claim 12wherein said antiferromagnetic coupling layer is Ru, Rh, or Ir.
 18. Themagnetic writer described in claim 12 wherein said antiferromagneticcoupling layer is Ru and has a thickness between about 3 and 10Angstroms.
 19. The magnetic writer described in claim 12 wherein saidantiferromagnetic coupling layer is Rh and has a thickness between about3 and 7 Angstroms.
 20. The magnetic writer described in claim 12 whereinsaid laminated write pole provides a write field of at least 10 kOe. 21.The magnetic writer described in claim 12 further comprising a layer ofNiFe between said lower ferromagnetic layer and said antiferromagneticcoupling layer.
 22. The magnetic writer described in claim 12 furthercomprising a layer of NiFe between said antiferromagnetic coupling layerand said upper ferromagnetic layer.